Layer 2 Virtual Private Network (VPN) technique based on Multi Protocol Label Switching (MPLS) (shortened hereinafter as MPLS L2VPN) can provide Internet Protocol (IP) services and Layer 2 VPN services simultaneously in one network, in which any rate can be set conveniently and the configuration is simple.
In the conventional MPLS L2VPN architecture, interworking of different Provider Edge (PE) equipment through heterogeneous link layer protocols is implemented to transmit data packets. At present, an IP-interworking technique between remote ends is adopted to implement the heterogeneous link layer protocol interworking in the MPLS L2 VPN. The Internet Engineering Task Force (IETF) defines a scheme of the IP-interworking in draft-kompella-ppvpn-12vpn-02 and draft-martini-12circuit-trans-mpls-09. The scheme implements the IP-interworking under heterogeneous link layer protocols by a negotiation between a local PE and a Customer Edge (CE) through a control plane, wherein, Asynchronous Transfer Mode (ATM) and Frame Relay (FR) are taken as layer 2 protocols for the links that two PEs access, respectively, and IP is taken as the network protocol for both links.
During reconstructions of old networks and upgrading of some old networks, networks of heterogeneous link layer protocols may be encountered by some enterprise users. For example, an enterprise has two CEs, and both of them adopt FR low-rate links to connect with each other through a PE previously. At present, one of the CEs is upgraded to the ATM high-rate link while the other desires to remain with the low-rate link. For the enterprise, the interworking of the heterogeneous link layer protocols is thus required for convenience. In addition, the interworking of the heterogeneous link layer protocols may facilitate the smooth upgrading of the network.
The interworking of homogeneous link protocols on local equipment can be implemented by a protocol defined in draft-kompella-ppvpn-12vpn-02, or Circuit Cross Connect (CCC).
However, the inventor found: since Border Gateway Protocol (BGP) cannot accommodate heterogeneous links in one VPN, the BGP can not support the interworking of local heterogeneous link protocols. In addition, CCC is a bridge equipment similar to local layer 2 switch and cannot translate different link-layer protocols, so the interworking of local heterogeneous link protocols cannot be implemented, either. Meanwhile, without the interworking of local heterogeneous link protocols, smooth upgrading of the network can not be achieved.